Color television

ABSTRACT

Color television signal detection apparatus utilizing only two synchronous detectors, the output signals of the two detectors, being combined with each other to derive a third signal of the same type as that provided by the synchronous detectors themselves, each of these signals then being combined with the luminance signal to provide the three desired signals representative of the color components.

United States Patent [191 Pritchard et al.

[111 3,820,157 June 25, 1974 COLOR TELEVISION Inventors: Dalton H.Pritchard, Princeton,

N.J.; Alfred C. Schroeder, l-luntingdon Valley, Pa.

Radio Corporation of America, Princeton, NJ.

Filed: July 25, 1952 Appl. No.: 300,855

Assignee:

U.S. Cl. 358/30, 358/23 Int. Cl. H04n 9/02 Field of Search 178/52, 5.4;

References Cited UNITED ST ATES PATENTS 2/l950 Seeley 250/27.l

- tive of the color components.

3/1953 Goldberg 178/54 2,728,813 12/1955 Loughlin 178/5.4 2,943,1426/1960 Loughlin 178/52 Primary Examiner-Richard Murray Attorney, Agent,or Firm-E. M. Whitacre; William H. Meagher 57 ABSTRACT Color televisionsignal detection apparatus utilizing only two synchronous detectors, theoutput signals of the two detectors, being combined with each other toderive a third signal of the same type as that provided by thesynchronous detectors themselves, each of these signals then beingcombined with the luminance signal to provide the three desired signalsrepresenta- 5 Claims, 3 Drawing Figures IE aemr PATENTEDJUNZS m43520,15?

SHEET 1 UF 3 ATTORNEY COLOR TELEVISION This invention relates toimprovements in color television receivers-and in particular toimprovements in synchronous detectors employed therein.

In one color television system the signal representing the requiredvideo information hastwo video components. One component representsvariations in brightness and corresponds in most respects to the signalheretofore employed in standard black and white television systems. Theother video component is a color carrier that is phase and amplitudemodulated in accordance with the hue and saturation of the colorrepresented.

One way of deriving the color carrier is as follows. The output of acolor oscillator of color carrier frequency is applied to a phasesplitter and each differently phased output of the phase splitter isamplitude modulated with signals representing different sets of colorinformation. Each set of color information may represent differentcombinations of the brightness component and the component colorsselected for the system. Usually red, green and blue are employed. Theoutput signals of the separate modulators are then combined to providethe desired color carrier. In order to save bandwidth, the frequency ofthe color carrier is so chosen and the upper frequency limit of thecolor information applied to the modulators is so set that the colorcarrier and at least some of its sidebands are within the upper portionof the frequency spectrum occupied by the brightness signal.

The color information conveyed by the color carrier and the portion ofits sidebands lying in the upper region of the video spectrum can berecovered at a receiver by applying the received signals lying in thisregion to a plurality of synchronous detectors which serve to heterodynethemwith different phases of the color carrier frequency. The sets ofcolor information provided by the synchronous detectors then may becombined with the total received signal so as to derive signalsrepresenting the selected component colors. These latter signals thenmay be applied to a suitable means for forming an image in color.

It has previously been suggested that the outputs of two synchronousdetectors be combined with the total received signal so as to derive twosignals, each representing the intensity variations of a differentselected component color. These two color signals were thensubtractedfrom the total received signal so as to derive a signalrepresenting a third selected component color. However, it has beenfound that the total received signal must be delayed in order to allowfor the delay caused by the apparatus that combined it with the outputsof the synchronous detectors so as to derive the signals representingthe first two selected component colors. Furthermore, when the signalrepresenting the third component color is derived in this manner, itsrelative amplitude to the other color signals may not be correct andthis required additional gain control apparatus.

In another previous arrangement, three synchronous detectors have beenemployed in such manner that when the output of each synchronousdetector is combined with thetotal received signal, a signalrepresenting one selected component color is produced. These signalshave proper time relations and proper relative amplitude. However, ithas been found advantageous to change at field rate the phaserelationships of the waves of color carrier frequency that are appliedto the different modulators at the transmitter. Thus during one field aparticular color maybe represented by one phase of the color carrier andduring the next field the same color may be represented by a differentphase. Therefore at the receiver, corresponding phase changes must bemade in the waves of color carrier frequency applied to the differentsynchronous detectors. Where such a color phase alternation system isemployed, the phases of the color carrier waves applied to two of thesynchronous detectors are generally interchanged. If only twosynchronous detectors are employed. the color phase alternation can besecured by changing the phase of waves of color carrier frequency thatis applied to one of them during successive fields. The equipment forproducing color phase alternation when two synchronous detectors areemployed is much simpler than the equipment required to produce colorphase alternation when three synchronous detectors are employed. Inaddition it is easier to adjust and operate. However, as pointed outabove, the use of two synchronous detectors requires additional delaycircuits in the channel carrying the total received signal as well asadditional gain controls.

It is therefore the object of this invention to provide an improvedcolor detection apparatus that employs only two synchronous detectors insuch manner as to avoid the necessity for additional delays and gaincontrols.

This objective can be achieved by combining the outputs of twosynchronous detectors with each other so as to derive a third signal ofthe same type but not necessarily of the same polarity as that providedby the synchronous detectors themselves. The output signal of the twosynchronous detectors are combined as previously described in connectionwith a prior arrangement so as to derive signals representing twoselected component colors. The third signal derived from the combinationof the outputs of the two synchronous detectors is also combined withthe total received signal so as to derive a signal representative of thethird selected component color. Thus it may be said that the third colorsignal'is deriveddirectly from the outputs of the two synchronousdetectors rather than from the signals representing only the selectedcomponent colors. As will become apparent from the detailed descriptionbelow,

this change in .the manner of deriving the third color signal alsopermits a simplification of equipment.

The details of the invention will be better understood after a detailedconsideration of the drawings in which:

FIG. 1 is a block diagram of one form of color television receiver inwhich this invention may be employed.

F IG. 2 is a schematic presentation of the synchronous detectors shownin FIG. 1; and

FIG. 3 is a schematic presentation of the combining and adding circuitsof- FIG. .1.

The present invention may be used advantageously in any color televisionsystem of the type set forth above, i.e., one in which the color carrieris modulated with sets of color information that contain components ofeach of the selected component colors. Many variations in the respectivecompositions of the brightness signal and the sets of color informationthat are applied to the modulators at the transmitter so as to formtheof the February 1952 issue ofElectronics.,. i

In this system, the transmitted signal E may'be de fined by thefollowing expression;

where E is the gamma correctedbrightness signalthat is comprised ofgamma corrected color signa'lsasindi- L cated by the expression: v i

where E E, andtE represent the green,red and blue gamma selectedcomponent color signalsrespectively and w is the frequency of the colorcarrierexpressed in radians. The color carrier maybe derivedduring onefield by modulating a zero degree phase "of thecolor carrier frequencywith a blue color difference signal E the amplifier 10, the band passfilter 12,;the potentionr phase of the color carrier frequency. his tobe understood that this zero degree phase is the; same phaseas the colorcarrier hasat the synchronousde'tector when; f

it is zero degrees at the transmitter. The manner in which this phase ofthe color carrier frequency is derived will be described below. If thetransmitted and received signal E,,, is as represented by the expressiona and-if the overall relative gain of the chroma control 8',

eter 14, the synchronous detector 16 and the lowpass filter 18 withrespect to the gain afforded by the signal E,,, by the delay line is2.03. the negative blue color 5 differencesignal E E is recovered; The'heterod'yn- .ingaction of thesynchronous detector produces upper and.lower sidebands and the lower sidehands containing' the color differencesignals in their original frequency is selected by a low pass. filter18. if the lowest frequency passed by the band pass filter 12 is notlower than the highest frequency passed by the low pass filter 18,nofrequencies of the signal Em will pass directly 7 A 7 through both ofthem. The negative bluecolor differ- E,, reduced by a factor of 2.03,i.e. 1.l4XTl 78in ex-. T pression a and a 90 phase ofa red colordifference sig-/ nal E,' thatis reduced by a factor of L14." During vthe next field the color carrier may be derivedby.,mod-

ulating a zero degree phase of thecolor carrier frequency with the sameportion of the blue color differencesignal E f-E as before but bymodulating 3 2 70 phase of the color carrier frequency with thesameportion of the red color difference signal E 'E /..The upperfrequency of the color difference signalsmay be limited to some lowvalue such as l megacycle'so'that.

the sidebands produced by the modulator in response to the colordifference signals lie within 1 megacycle on 1 each side of the colorcarrier frequency it). As a is generally placed rather high in the videospectrum of the brightness signal, the color information represented bythe sidebands lies in the upper portion of the video y spectrum. Duringeach field the outputs of the modulators are combined toform, the colorcarrierandit 'is added to the brightness signal E The brightness signalE is itself derived by adding the different color signals in theproportions indicated by theexpression b. The.

portion of the color difference signals applied to" the modulators isindicated by the coefficients of the ex-- pression a. a

One form of receiver that may be used toreproduce images in color fromthe signal E and whichembodies the present invention is illustrated inthe block diagram 7 of FIG. 1. The signal E, is recovered by anysuitable signal detector 2, anda desired portion of it is supplied to avideo amplifier 4 via a contrast control 6 that is shown as apotentiometer. The output of the'video amencesign'al-.E ,,E,, thatappears at the output of the low pass filter 18 is then applied totheblue combining a circuit 7. The signal E appearing at the output of thevideo amplifier' t is delayed by a delay line 5 by the same amount that.the negative blue color difference signal Elk-E is delayed in passingfrom ,the'output of the'video amplifier 4' to the input o'f thecombining .cir-

' cuit 7..Thus the signal E' and the.negativecolordiffen ence signalE,,-Ei, arrive at-the input of the. combining circuit 7 in propertimerelationship. Thezgain of the blue synchronous detector 16 isgenerally-made greater 7 than the maximum required so that thechromacontrol 8 can be adjusted to increase or decrease the relative 1 jamplitude of the color difference signal with respect to I the signalEln this way the amplitude of the bright ness component E in the;signaliEm Can be made; equal to the amplitude of'the correspondingbrightnesscomponent E,, in the negative blue color difference signal.With the polarities indicated the subtractionof the signal E, from thenegativecolor difference signal E 5,,"

yields (c) E .,"E,,-E,, -.(A.C. components ofexpres- V sion a). The AC.components maybe termed mixed 7 highsMy as they are the high. frequencycomponentsof all colors combined; The; low; frequency -brightnesscomponents of E and -E cancel out. The high fre- 7 quency componentsM;,--of-E pass through the. combiner 7. The signals. at the output ofthe combiner 7 including the high frequency portion -My'ofthe Ibrightness signal E,/ and the low frequencyicolor signal -E,, areclamped in normal manner by-a.d;c.. resto ration or clamp circuit 24before being applied tom plifier is appliedvia a delay lineS to abluecombining circuit 7. A desired portion of the output of the videoamplifier is selected by a chroma control 8, here shown as apotentiometer, and is coupled via an amplifier. 10 to a band pass filter12 that is designed topass frequenelectrode of a color kine'scope 26that controls the in tensity of the blue light emitted by the kinescope.

In order to recover the red signal E the following operation isperformed. The output of the band pass.-

filter 12 is coupled via a potentiometer 28 to a redtsynchronousdetector 30 wherein itis heterodyned during 7 successive fields with 90and 270 phases of the color carrier frequency thatare derived in amanner to be described. Two sidebands are produced" byfthe modulacies inthe upper region of the video spectrum occupied a by the sidebandscontaining'the color information; A

. portion of the output of the band passfilter l2 iscou-- pled by apotentiometer l4 to a blue synchronousde tector 16 wherein it isheterodyned'witha zerodegree bined with the total received. signal Em{seeexpressiontion' process and the lower one containingthe original 1frequencies of the negative red color difference signal 7 E F-E, thatwas applied "to one of the modulators at the transmitteris selected by alow pass filter 32 and is ap V plied to a red combining circuit 34'where it i s-com- I a) in such manner as to cancel out the low frequencyportion of the brightness signal E andiproduce the low frequency redcolor signal -E,'. This signal, the high frequency portion M of -E andthe color carrier and its sidebands are all clamped in a normal mannerby a clamp circuit 36 before being applied to an electrode in thekinescope 26 that controls the intensity of the red light emitted.

In previous arrangements employing only two synchronous detectors thelow frequency signals E,, and E, appearing at the outputs of thecombining circuits 7 and 34 were added to the signal E so as to derivethe green color signal E, M and an additional amount of delay had to beintroduced in the signal E so as to compensate for the delay produced bythe adders 7 and 34. The delay was increased because of the peakingrequired in the adder circuits to achieve proper gain. Then, because thebrightness component E of the total received signal was comprised asindicated in the expression b, the amplitudes of the signals E,,' and E,that were added to the total received signal E had to be changed.

In accordance with one embodiment of this invention, the negative redcolor difference signal 0.51

(E f-E and the negative blue color difference signal 019 (E 'E areinverted in separate sections of an inverter 39 and added in an adder 38so as to derive a negative green color difference signal E E Inasmuch asonly fractional amounts of the color difference signals are required,the adder 38 does not have to furnish any gain and therefore peakingcircuits that introduce delay are not required. The negative green colordifference signal E,,-E is then applied to a green combining circuit 40where it is combined with the signal E, so as to produce the green colorsignal E,,', as well as the mixed high signal M,,. This signal isclamped by a circuit 42 and applied to an electrode of the kinescope 26that controls the amount of green light emitted.

In the receiver just described the negative color signals E,,, E, andE,, emerged from the various combining circuits. If positive colorsignals are required the amplifier 10 of FIG. 1 could be a cathodefollower so that the polarity ofthe color signals would not be reversedand the outputs of the synchronous detector would be the originalpositive color difference signals E,,E,, and E E,,. In order to cancelthe E,, term in thecombining circuits any known means for inverting thesignal E, could beemployed. I

The combining circuits of FIG. 1 may serve to subtract the colordifference signal from the total signal. However, the broad concept ofthe invention whereby the color difference signals are so combined so asto derive a third color difference signal can also be realized by usingcombining circuits that add the two color difference signals. In such anarrangement a positive selected component color signal is derived byadding a positive color difference signal such as E to a positive totalsignal E,,, so that the low frequencies of the E,, component of thecolor difference signal cancels out the low frequencies of +E,,component of E,,,. If a negative selected color signal is desired, thepolarities of both the color difference signal and the signal E,, arereversed.

It is apparent that some means must be provided for supplying the 0phase of the color carrier frequency to the blue synchronous detector 16during every field 6 and the 90 and the 270 phases to the redsynchronous detector during successive fields in fixed phaserelationship with the corresponding phases supplied to the modulators atthe transmitter. One way of conveying the synchronizing information isto transmit a burst of 90 phase of the color carrier frequencyimmediately following each horizontal sync pulse as described in a U. S.Pat. application to Bedford that was filed on Feb. 11, 1950 and bearsthe Ser. No. 143,800. A similar method is also described in "Electronicsfor February 1952 at page 96. The burst may be used in a variety of waysto control the phase and frequency of a local color oscillator 44. Inour U. S. Pat. application bearing Ser. No. 300,854 filed on July 25,1952, for example. advantage is taken of the fact that during the burstinterval the output of the blue synchronous detector 14 is zero if thecarrier frequency wave applied to the blue synchronous detector is 0. Ifthe local color oscillator varies in phase in one direction, the outputof the blue synchronous detector during time of burst becomesproportionately positive and if the oscillator shifts in phase intheopposite direction, the input of the blue synchronous detector becomesproportionately negative. Then voltages are applied so as to control thefrequency and phase of the oscillator. The output of the localoscillator is applied to the blue synchronous detector 14 via a bufferamplifier 48. In order to obtain the phase alternation between 90 and270 the output of the buffer amplifier 48 is coupled to the redsynchronous detector 30 via a color phase alternation circuit 50described in U. S. Pat. application No. 300,853 filed on July 25, 1952in the name of Dalton H. Pritchard and Alfred C. Schroeder.

A sensing circuit 52 provides, in response to the flyback pulsesoccurring in the horizontal deflection circuit 49 and the output of astandard sync separator circuit 54, a control signal that serves tochange the phase appearing at the output of the color phase alternationcircuit from 90 to 270 at field rate. The field sensing circuitdistinguishes the even-numbered line fields from the odd-number linefields.

The scanning of the beams in the kinescope 26 is controlled in any knownmanner by a horizontal oscillator and AFC circuit 56, the horizontaldeflection circuit 49, a vertical integrating network 58, a verticalblocking oscillator 60, a vertical deflection circuit 62 and a yoke 64.

FIGS. 2 and 3 illustrate the details of a circuit employing a minimumnumber of components for extracting the negative color signals E,,, E,and E,,' from the color carrier. The signals supplied by the chromacontrol 8 of FIG. 1 appear at the terminal A. After passing through theamplifier 10, the upper region of the signal E,, in which the colorcarrier and portions of its sidebands lie is selected by a standardconstant K band pass filter 12. The potentiometers 14 and 28 areconnected in parallel with the second parallel tuned circuit and thelower end of both potentiometers and the parallel circuit are returnedto a slight negative voltage which may be 3 volts as indicated. Themoveable arms of each of the potentiometers 14 and 28 are respectivelyconnected to similar terminals of unilattentiometers l4 and 28 areconnected to terminals 70 and 72 by the resistors 74 and 76. Terminals78and 80 are commonly connected to a source of negativevoltage, hereshown as minus 3 volts. A source of the zero degree phase of the'colorcarrier frequency, for exampled between the, terminals 70 and 78. Theoutput of the color phase alternation circuit 50 is coupled be- V du'cesthe'red color signal f-E These twosignalsare. ii

V ple the oscillator and buffer amplifier ofFlGai is con-i tween theterminals 72 and 80 so that a 90 phase of the colorcarrier frequency isapplied betweenetheseterminals during one field and a 270 phase of thecolor car'- rier frequency is applied between them during the-nexttentiometers 14 and 28. I

The unilateral devices serve to heterodyne the upper region of the videospectrum that islse'le'ctedfbiy the band pass filter 12 so as to produceupper and lower sidebands across the load resistors 74 and 76. These 84of a'dual triode tube via parallel resonant circuits 86 and 88 that aresharply tuned to the color carrier frequency. In order to minimizeerrorsdue to phase quadrature, the color carrier frequency applied tothe unilateral devices is several times the peak amplitude of the color signalsapplied to the unilateral devices via the potentiometer. The parallelresonant circuits 86 and 88 isolate'the grids of the tubes from thesources of carrier frequency and yet permits the sidcbands to pass. The3 volts on the terminals 78 and 80reach the grids through the inductivebranches of the resonant circuits and thus serveto bias the tubes. Y a

The low pass filters 18 and 32 that are coupled in se ries with loadresistors 90 and 92 between the plates of the respectivetriode-sections82and .84 and 3+ serve" to attenuate any carrierfrequency that may be present as well as the upper sidebands produced bythe hetero sidebands. areapplied to the grids of thesectionsfiZ and pledto the output of said band pass filterfor synchro nouslydemodu'latingfsaid subcarrier wave to separately a t dyning action ofthe unilateral devices. Thusas previously explainedthe negative bluecolor difference sige nal E,,E,, appears across the resistor andthe redcolor difference signal appears across the resistor 92.

I These signals are coupled to the'combiningcircuits.

shown in FIG. 3 via leads 94 and 96 respectively.;-"

in FIG. 3, thesignal E, appearing at pointBof FIG.

odes 98, and 102.,The lead 94ibearingthenegative blue color differencesignal E ',-'E,, is coupled toithe right hand section of the dual triode98 and thelead 96,

bearing the negative red color difference signal E E,, is coupled to theright hand sideof the dual triode 100.

Due to the cathode coupling, these same color difference signals appearon the cathodes of the left hand ference between the signal E,,, that isapplied to the grids and the color difference signal applied tothecathodes. As noted in the discussion'of FlG'. [,Ihfsig- 7 nalis a purecolor signal plus the mixed highs-M Thus the left hand section of thedual triode 98 "yields 9 a low frequency signal E ,v and a highfrequency/ signal ,M,,' which is a mixture ofthe highfrequencylcomponcnts ofthe signals E,,, E/ and E,, in the amplituderatios of these color components illustrated in" the expression -b.- Inlike manner, the dual triode @100 pro-- 1 is coupled tothe left handside of eachtof'the dual trir sections of the d u'al triodeswith thesame polarityfand a hencethe output of the'left hand sections yieldthe'diffor impressing said three color differencesignais re-.spectivelyupon the input cireuitsef'saidtubesto'pro clamped'inconventional manner by the clamp circuits" 241 and 36 before beingapplied to the kinescope that forms the images in color.-

Before deriving the green color signal E thenega y Combining apredetermined proportion of the color 7 difference signals E,,"E. andE,' in an adding device 38, which. as shown in H6. 3'may take the formof Potentiometers l04-and l06z-connected-as shown;

Other forms of adders may be employed tocombine the signalsin thismannen but as only fractional amounts of the blue and red colordiffereneesignalsare I required, the adder'need not be inthefor niofanampli tier.

cathode coupled to the left half so asto' be subtracted I Thenegativegreen color difference*signai E FEy Y applied to the" right half of thedual triode 1022 andis from the signal E that is applied'to the grid ofthe left 7 hand triode. This yieids thc signer-F 15,, which is'clampedby the clamp circuit 42 before being appliedto the kinescope. V

is. V

1. In a' color television receiver adapted to receive a composite signalincluding a brightness signal and a color component comprising asubcarrie'rwave modu-- latedin phase in accordance wi'tha plurality ofcolor difference signals representative of the color of an ob ject, thecombination including: a band pass filter for selectively passingcomposite" signal frequencies in a Having thus describe d theinventionwhat is ciaimed 1 1. V I i band occupied by said color component; meanscou-. I

derive first and second color difference signals; a signal-addingnetwork including a pair of resistors; means t for impressing saidderived color difference signals respectively upon said resistors; saidres-istors being con r c I nected together to a common terminal at whichto develop a third color'difference signal; a delay line. for

said composite signal providing a delayed brightness signaloutputiandatrio of signal'combiningcircuits of r similar configuration,each being coupled to receive said delayed brightness signal and arespectively differs tent one of said three color difference signals. I2. In a color teievision receiveradapted to receive a composite signalincluding a brightness signal and a subcarrier wave modulatedtinquadrature phases re-' spectively in accordance with two colordifferencesigi I r nals representative respectivelyof two color aspectsof an object, the combinationincluding; a, bandpass filter r I forselectively passing composite; signal frequenciesv in a band occupiedvbysaid color component; individual;

means coupled to the output of said band pass filter for synchronouslydemoduiating said subcarrier wave to separatelyderivesaidtwocolordifferencesi nals from said composite signal; asignal-adding network includ ing two resistors; means for impressingsaid two derived 7 7 color differencesignals respectively upon said two'I8- I i sistors, said "resistors beingconneeted togetherto a commonterminal at which to develop a third color difference signal;three'electron tubes, each having an I I input circuit andtan outputcircuit;mcnns including a delay line for impressing'said receivedbrightness signal upon the input circuitsof all of said tubes; andmcansduce three component color representative signals in the respectiveoutput circuits of said tubes.

3. In color television receiver apparatus, the combination of a sourceof monochrome signal, a source of first color difference signal, asource of second color difference signal, a first mixer circuitcomprising an electron discharge device having a plurality of inputs, asecond mixer circuit comprising an electron discharge device having aplurality of inputs, a third mixer circuit comprising an electrondischarge device having a plurality of inputs, with said source ofmonochrome signal connected to one of the inputs ofeach of said first,second and third mixer circuits, with said source of first colordifference signal connected to another of the inputs of the first mixercircuit, and with the source of the second color difference signalconnected to another input of the third mixer circuit.

4. ln color television receiver apparatus adapted for the reproductionof a televised picture from a composite color signal including amonochrome signal and a color sub'carrier, the combination ofamonochrome signal source, a first color difference signal source, asecond color difference signal source, a first mixer circuit comprisinga first dual-triode electron discharge device having a pair of anodes, apair of cathodes and a first and second control grid, a second mixercircuit comprising a second dual-triode electron discharge de-' vicehaving a pair of anodes, a pair of cathodes and a first and secondcontrol grid, a third mixer circuit comprising a third dual-triodeelectron discharge device having a pair of anodes, a pair of cathodesand a pair of control grids, said monochrome signal source beingconnected to one of the control grids of each of the first and seconddual-triode electron discharge devices, with the first color differencesignal source connected to the other control grid of the firstdual-triode electron discharge device, and with the second colordifference signal source connected to the other control grid of thesecond dual-triod electron discharge device.

5. A monochrome signal source, a first color difference signal source, asecond color difference signal source, a first mixer circuit having aplurality of inputs, a second mixer circuit having a plurality ofinputs, and a third mixer circuit having a plurality of inputs, withsaid source of monochrome signal connected to one of said inputs of eachof the first and third mixer circuits, and with said source ofmonochrome signal being connected through a delay line to one of theinputs of the second mixer circuit.

1. In a color television receiver adapted to receive a composite signalincluding a brightness signal and a color component comprising asubcarrier wave modulated in phase in accordance with a plurality ofcolor difference signals representative of the color of an object, thecombination including: a band pass filter for selectively passingcomposite signal frequencies in a band occupied by said color component;means coupled to the output of said band pass filter for synchronouslydemodulating said subcarrier wave to separately derive first and secondcolor difference signals; a signal-adding network including a pair ofresistors; means for impressing said derived color difference signalsrespectively upon said resistors, said resistors being connectedtogether to a common terminal at which to develop a third colordifference signal; a delay line for said composite signal providing adelayed brightness signal output; and a trio of signal combiningcircuits of similar configuration, each being coupled to receive saiddelayed brightness signal and a respectively different one of said threecolor difference signals.
 2. In a color television receiver adapted toreceive a composite signal including a brightness signal and asubcarrier wave modulated in quadrature phases respectively inaccordance with two color difference signals representative respectivelyof two color aspects of an object, the combination including: a bandpass filter for selectively passing composite signal frequencies in aband occupied by said color component; individual means coupled to theoutput of said band pass filter for synchronously demodulating saidsubcarrier wave to separately derive said two color difference signalsfrom said composite signal; a signal-adding network including tworesistors; means for impressing said two derived color differencesignals respectively upon said two resistors, said resistors beingconnected together to a common terminal at which to develop a thirdcolor difference signal; three electron tubes, each having an inputcircuit and an output circuit; means including a delay line forimpressing said received brightness signal upon the input circuits ofall of said tubes; and means for impressing said three color differencesignals respectively upon the input circuits of said tubes to producethree component color representative signals in the respective outputcircuits of said tubes.
 3. In color television receiver apparatus, thecombination of a source of monochrome signal, a source of first colordifference signal, a source of second color difference signal, a firstmixer circuit comprising an electron discharge device having a pluralityof inputs, a second mixer circuit comprising an electron dischargedevice having a plurality of inputs, a third mixer circuit comprising anelectron discharge device having a plurality of inputs, with said sourceof monochrome signal connected to one of the inputs of each of saidfirst, second and third mixer circuits, with said source of first colordifference signal connected to another of the inputs of the first mixercircuit, and with the source of the second color difference signalconnected to another input of the third mixer circuit.
 4. In colortelevision receiver apparatus adapted for the reproduction of atelevised picture from a composite color signal including a monochromesignal and a color subcarrier, the combination of a monochrome signalsource, a first color difference signal source, a second colordifference signal source, a first mixer circuit comprising a firstdual-triode electron discharge device having a pair of anodes, a pair ofcathodes and a first and second control grid, a second mixer circuitcomprising a second dual-triode electron discharge device having a pairof anodes, a pair of cathodes and a first and second control grid, athird mixer circuit comprising a third dual-triode electron dischargedevice having a pair of anodes, a pair of cathodes and a pair of controlgrids, said monochrome signal source being connected to one of thecontrol grids of each of the first and second dual-triode electrondischarge devices, with the first color difference signal sourceconnected to the other control grid of the first dual-triode electrondischarge device, and with the second color difference signal sourceconnected to the other control grid of the second dual-triod electrondischarge device.
 5. A monochrome signal source, a first colordifference signal source, a second color difference signal source, afirst mixer circuit having a plurality of inputs, a second mixer circuithaving a plurality of inputs, and a third mixer circuit having aplurality of inputs, with said source of monochrome signal connected toone of said inputs of each of the first and third mixer circuits, andwith said source of monochrome signal being connected through a delayline to one of the inputs of the second mixer circuit.